Certain embodiments of the present invention generally relate to an electron beam tomography system, and more particularly to a collimator for a dual-slice electron beam tomography system.
Computerized tomography (CT) systems produce planar images along imaginary cuts, or slices, through a patient. CT systems typically include an x-ray source, which revolves about an imaginary axis through a subject. After passing through the subject, the x-rays impinge on an opposing array of detectors.
Typical CT patient scans are executed in either an axial mode or in a helical mode. In axial mode, the table that supports the patient stops, the scan is executed, and then the table moves to a new location. In helical mode, the patient table continuously moves throughout the course of the scan. Single slice scanners (scanners having one detector array) are common, and dual slice CT systems (systems having two detector arrays) are known.
Some CT scanners include a scanning electron beam x-ray source, such that an electron beam is magnetically deflected so as to rotate in a generally arcuate path, and in doing so, impinges upon an arc-shaped target. As the electron beam impinges on the target, a source of x-rays is generated. As the electron beam moves, so does the source of x-rays. The x-rays encounter a collimator which passes a portion and blocks a portion of the x-rays. The x-rays are shaped into a fan beam by the collimator and then intercepted by a ring-shaped detector array on an opposite side of the patient. U.S. Pat. No. 4,352,021 (xe2x80x9cthe ""021 patentxe2x80x9d), issued Sep. 28, 1982, discloses such an electron beam scanner. However, in order to collimate the x-ray fan beam at different widths, multiple collimators having different sized apertures were typically needed, thereby increasing the cost of the system.
U.S. Pat. No. 5,442,673, issued Aug. 15, 1995 (xe2x80x9cthe ""673 patentxe2x80x9d), discloses an x-ray collimator for use within an electron beam computed tomography (EBT) scanner, in which a rotating electron beam is directed to impinge upon a ring shaped target. The ""673 patent discloses variable tomographic slice width for a single slice EBT system. Single slice EBT systems, however, take longer to scan a given number of slices than corresponding dual slice systems.
Thus, a need exists for a more efficient method and apparatus for achieving EBT scanning.
Embodiments of the present invention provide an electron beam tomography (EBT) scanning system comprising an electron source, a target ring, first and second detector arrays, and a collimator. The electron source generates an electron beam, which is received by the target ring. The target ring emits an x-ray fan beam upon impingement of the electron beam on the target ring. The first and second detector arrays are arranged opposite the target ring and detect the x-ray fan beam. The collimator is arranged concentrically between the target ring and the first and second detector arrays. The collimator has interior and exterior walls concentrically arranged with one another and surrounding a patient examination area. The interior and exterior walls have first and second sets of apertures. The first set of apertures are aligned to collimate the x-ray fan beam into a first collimated beam having a first width. The first collimated beam may be detected by first and second detector arrays when the collimator is in a first position. The first collimated beam may be detected by one of the first and second detector arrays when the collimator and detector are moved to a second position. The second set of apertures are aligned to collimate the x-ray fan beam into a second collimated beam having a second width. The second collimated beam may be detected by the first and second detector arrays when the collimator is moved to a third position. The collimator is moved between the first, second, and third positions with respect to the target ring to define the first and second collimated beams having the first and second widths, respectively.
The collimator also includes a detector-only region, a source-only region and a source/detector overlap region. The detector-only region has a first set of post-patient x-ray apertures for shielding the detector from scattered x-rays when the beam has a first width; and a second set of post-patient x-ray apertures for shielding the detector from scattered x-rays when the beam has a second width. The source/detector overlap region has a first set of pre-patient x-ray apertures for collimating the x-ray fan beam into the first collimated beam at the first width and a first set of post-patient x-ray apertures for shielding the detector from scattered x-rays. Additionally, the source/detector overlap region has a second set of pre-patient x-ray apertures for collimating the x-ray fan beam into the second collimated beam at the second width and a second set of post-patient x-ray apertures for shielding the detector from scattered x-rays. The source-only region has a first set of pre-patient x-ray apertures for collimating the x-ray fan beam into the first collimated beam at the first width; and a second set of pre-patient x-ray apertures for collimating the x-ray fan beam into the second collimated beam at the second width.